As previously stated, this research project was designed to purify human renal renin from cadaver kidney in order to: (1) characterize human renin as an enzyme and protein, (2) develop a direct radioimmunoassay for renin to clarify its role in the pathogenesis of human hypertension, and (3) study the relationship of renin to its precursor form(s). Having accomplished the complete purification of human renal renin, we have, over the past year, attained higher yields of pure renin thus enabling the generation of highly specific antirenin antibodies and the development of a direct renin radioimmunoassay. This represents to our knowledge the first direct measurement of human renin reported to date. We plan, based on the above results: (1) to utilize antirenin antibody, to effect large-scale purification of human renal and plasma renin, as well as the larger molecular weight form of renin previously isolated in our laboratory; (2) to characterize further renin and its larger molecular weight form by amino terminal amino acid sequencing; (3) to apply the direct renin radioimmunoassay to the measurement of renin in both tissue homogenate and human plasma, correlating these measurements with angiotensin 1 determinations; and (4) to continue correlative work on the mechanism(s) of activation of renin precursor and the role of renin in experimental models of hypertension in animals.